A Sample-Collection Device for SEM Imaging and Analysis of Coke Deposits from Lubricant Thermal Degradation
Abstract
Solid deposits form when a lubricant undergoes thermal breakdown due to high-temperature conditions and can cause adverse operational effects within engines. A collection device designed to allow coke to form on its surface was inserted inside of a test section to further study the physical characteristics of coke. The device was made from 0.003-inch-thick stainless steel 304 and went through several designs of varying cut-out shapes to form a test strip. The material of the coke-collecting test trip is the same as the test section. Three different lubricants were analyzed using a scanning electron microscope (SEM): a synthetic-blend motor oil (SAE 20W-50), a flushing/rust preventative oil, and Mobil DTE 732 which is a turbine oil. In each test, 400 mL of lubricant was circulated at 10.4 mL/min through a test section that is heated to 475 °C. Nitrogen was used to purge the system to study the effects of pyrolysis. The addition of the test strip into the test section was determined to not have a significant effect on the induction time when comparing two Mobil DTE 732 tests with and without the test strip. Two additional tests were conducted with motor oil at 445 °C to generate an Arrhenius plot of induction time. The elemental composition of each degraded oil was analyzed on the test strip using energy-dispersive spectroscopy (EDS). Differences in the microscopic structure of each oil was observed. The elemental composition for coke from turbine and motor oils was found to mostly consist of carbon, as expected. The usual additives of P, S, Ca, Zn, and Ba were found in the flushing/rust-preventative solid deposits. For the turbine deposits, the additives of P, Si, S, Ca, and Zn were identified. Lastly, for the synthetic-blend motor oil, additives of P, Mg, S, Ca, and Zn were detected.
Citation
Gutierrez, Noble Knight (2023). A Sample-Collection Device for SEM Imaging and Analysis of Coke Deposits from Lubricant Thermal Degradation. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /199025.